ASCL1 and small cell lung carcinoma: Based on previous work by our laboratory and others, SCLC has been classified into five tumor cell subtypes characterized by eponymous transcription factors ASCL1 (SCLC-A and SCLC-A2), NEUROD1 (SCLC-N), YAP1 (SCLC-Y), or POU2F3 (SCLC-P) (8, 9, 20–23).